Linear Alpha Olefins represent an important class of industrial chemicals with a wide range of applications. They are used as co-monomers for ethylene polymerization as well as precursors to plasticizers, lubricants, and surfactants. Currently, these olefins are mainly produced by oligomerization of ethylene, which, in turn, is derived from petroleum. As the world's oil reserves continue to diminish, development of renewable feedstocks for the production of alpha olefins becomes increasingly important. One obvious choice is ethylene from biomass-derived ethanol. A more direct method is the decarbonylative dehydration of long chain fatty acids. The latter route is particularly attractive because fatty acids are inexpensive and readily available starting materials derived from many natural sources. Since natural fatty acids contain an even number of carbon atoms, their corresponding alpha olefins will be odd-numbered after decarbonylative dehydration. Moreover, conventional ethylene oligomerization processes deliver only even-numbered alpha olefins, and odd-numbered olefins are largely inaccessible. These odd-numbered olefins are valuable building blocks in the synthesis of various fine chemicals such as lepidopteran insect pheromones, but are currently far too costly to be practical. Therefore, the development of an efficient and economic process for fatty acid decarbonylation is highly desirable.
Many strategies to convert fatty acids to alpha olefins have been pursued. Lead tetraacetate-mediated oxidative decarboxylation is a classical method. Alternative protocols that avoid stoichiometric toxic reagents have also been developed, such as Kolbe electrolysis and silver-catalyzed oxidative decarboxylation. However, these reactions proceed through highly reactive radical intermediates, and thus suffer from low yields due to many side reactions. A more recent approach entails the transition metal-catalyzed decarbonylative dehydration of fatty acids. A variety of transition metals including rhodium, iridium, palladium, and iron have been shown to catalyze decarbonylative dehydration reactions. To date, palladium has demonstrated the highest activity, and catalyst loadings as low as 0.01 mol % have been reported independently by Miller and Kraus. Unfortunately, their methods require very high temperatures (230-250° C.). In addition, it is necessary to distill the olefin product from the reaction mixture as soon as it is formed in order to prevent double bond isomerization, and therefore only volatile olefins can be produced this way. Decarbonylation processes under milder conditions have been developed independently by Gooβen and Scott. Although their reactions proceed at 110° C., much higher palladium catalyst loading (3 mol %) and an expensive, high-boiling-point solvent (DMPU, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone) are required.
The present invention addresses at least some of these deficiencies in the art.